A primary goal of this laboratory is to advance our understanding of cytokine-mediated tumor cell proliferation, with the ultimate goal of identifying targets for therapeutic intervention. For our studies we have focused on IL-6-dependent myeloma growth, a well characterized model of cytokine-dependent malignancy. We are performing studies aimed at (1) the characterization of the IL-6 receptor complex, (2) elucidating the mechanisms by which IL-6 regulates the action of growth-related genes, and (3) analyzing the mechanism by which tumor cells progress to a growth factor-independent phenotype. We have continued the structural characterization the IL-6 receptor on various cell types. Affinity crosslinking studies in our laboratory indicate that (1) a 130 kDa molecule associates directly with IL-6 and (2) the functional receptor complex may consist of dimers of gp80 plus two molecules of IL-6 and at least one gp 130 molecule. Studies using monoclonal antibodies developed in this laboratory also reveal that polymorphic forms of the IL-6 receptor complex exist on different cell types and may thus allow myeloma cells to be distinguished from normal cells. We are characterizing IL-6 regulated genes that participate in the control of IL-6-dependent cell proliferation. The expression of the immediate-early response gene jun-B is known to be upregulated in IL-6-dependent myeloma cells. Using antisense oligonucleotides to jun-B we have found that jun-B is essential for proliferation and survival in these cells. We have initiated studies to identify and characterize the IL-6 responsive elements in the jun-B promotor. Initial results indicate these elements reside in a region 540 base pairs upstream of the transcriptional start site. Our studies reveal that the progression to IL-6-independence is often mediated by a nonautocrine mechanism. Restoration of IL-6-dependence by the introduction of normal (wild type) DNA via cell fusion suggests that a negatively acting, growth regulatory gene is lost during the transition to IL-6-independence. In order to identify the chromosome on which this gene resides, we are screening a large panel of IL-6-dependent and IL-6-independent hybrid lines, derived by fusing IL-6-independent rat myeloma cells with normal mouse B lymphocytes. Identification of the chromosome will contribute to the molecular cloning of the gene responsible for transition to autonomous growth.